The U.S. Defense Department’s testing office is warning that the costs to operate and support the F-35 will significantly increase unless reliability of the aircraft improves, the Bloomberg news service is reporting.

Bloomberg’s Anthony Capaccio has obtained a copy of a May 8 presentation written for the DoD. The availability of spare parts for the 203 F-35s already assigned to bases “is getting worse, affecting fly rates” and pilot training, Capaccio writes. Reliability of parts is being questioned, the presentation from the Director of Operational Testing added. Repairs to defective parts is taking too long.

Reliability metrics linked to “critical failures have worsened over the last year,” as improvement “has stagnated,” Bloomberg noted.

In response, the F-35 program office pointed out that estimates of annual operating costs have decreased between 2.2 per cent and 4.2 per cent, depending on the F-35 model. “These reductions were the result of improved maintainability and sustainability as the weapons systems matures, the design stabilizes and maintenance” becomes more efficient and effective, Bloomberg news was told.